Light fixture with multimode optical output

ABSTRACT

A light fixture is provided with increased light output, uniformity of brightness and color and controlled lighting non-lambertian distributions by use of an optical element that functions simultaneously as an outcoupling TIR light guide and a direct throughput lens. It provides typical benefits of an edgelit light guide design including thin forms and shallow depth, extended emitting area, and single or dual peak off axis light distributions particularly useful in applications such as indirect illumination of ceilings, wall washing, aisle lighting, exterior façade lighting and area lighting as well as other lighting applications. Additionally, areas typically dedicated to bezels or edge reflectors can be greatly reduced or eliminated due to decreased hotspotting to provide a fixture face with very high percentage of light emitting area. Embodiments are described for direct, indirect, and direct indirect configurations.

RELATED APPLICATIONS

This application is a continuation in part of US non-provisional utility application 16/039,320 filed Jul. 18, 2018 now U.S. Pat. No. 10,852,466 which itself claims the benefit of U.S. provisional patent application Ser. No. 62/534,187 titled “Lighting Subassembly With Dual Mode Optical Element” filed Jul. 18, 2017.

SUMMARY

Light fixture embodiments provide benefits of increased light output, uniformity of brightness and color by use of optical elements that functions simultaneously as an outcoupling TIR light guide and a direct throughput lens. Provided are typical benefits of an edgelit light guide design including shallow depth, extended emitting area, and off axis light distributions such as batwing distributions particularly useful in downlighting and other lighting applications. Additionally, area dedicated to bezels or edge reflectors can be greatly reduced or eliminated due to decreased hotspotting to provide a fixture face with very high percentage of light emitting area. Some embodiments can be configured as direct/indirect light fixtures.

BACKGROUND

Lighting systems incorporating optical waveguides positioned close to the light source provide significant benefits such as thin form factor and adjustable lighting output. However, efficient optical coupling from the light source to the waveguide is difficult to achieve and typically 10% to 30% of light is lost. Traditional approaches that target full edge coupling of light into optical waveguides typically lose efficiency by having low utilization of uncoupled light and of light that enters the input edge but escapes light guide on a non-output face or near the edge where the output is blocked by a bezel or reflector. Often bezels are deemed necessary to hide “hotspotting”, non-uniform brightness close to light sources due to excessive outcoupling near the edge. In addition, light sources such as LEDs often have a variation of their color output over angle that are typically accentuated by coupling into optical light guides.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is perspective view of a ceiling mounted light fixture embodiment.

FIG. 1b is a perspective view of a suspended light fixture embodiment.

FIG. 2 is a cross section view of a light fixture with a conventional planar light guide.

FIGS. 3A and 3B (enlargement view) are cross section views of a light fixture configured with an optical element having angled input edges and an overhang feature at the input edges.

FIG. 4 is a digital image of a Reference A light fixture representing a conventional edgelit light guide construction as shown in FIG. 2 but without a bezel or cover lens.

FIG. 5 is a digital image of Embodiment A light fixture shown in FIG. 3A and FIG. 3B but without a bezel or cover lens.

FIG. 6 is a graph and table comparing quantitative metrics of Ref A vs. Embodiment A for characterizing brightness values along the line scan paths for direct transmission shown in FIG. 4 and FIG. 5.

FIG. 7 is a graph and table comparing quantitative metrics of Ref A vs. Embodiment A for characterizing brightness values along the line paths for initial reflection shown in FIG. 4 and FIG. 5.

FIG. 8 is a polar plot of embodiment A with one side only LED strip on and the light fixture oriented down as a direct lit downlighting fixture.

FIG. 9 is a polar plot of embodiment A with LED strips on both sides on and the light fixture oriented down as a direct lit downlighting fixture.

FIG. 10 is a cross section detail view of an embodiment with two optical elements configured to receive light from a central light source structure.

FIG. 11 is a cross section detail view of an embodiment with two optical element input faces within a recessed cavity.

FIG. 12 is a cross section view of a light fixture embodiment having an input face/output face alignment angle configured to direct a significant portion of light out the opposing face to be subsequently reflected out the output face.

FIG. 13 is cross-section perspective view of a direct/indirect light fixture embodiment with an x-y profile geometry linearly extruded in the z-axis to create a generally rectangular fixture shape

FIG. 14 is a cross-section perspective view of a direct/indirect light fixture embodiment with the x-y profile geometry is rotated to produce a generally circular shape fixture.

FIG. 15 is a cross-section view of a light fixture embodiment having 2 input faces with differing input face/output face alignment angles.

FIG. 16 is a view of a direct/indirect light fixture embodiment.

FIG. 17 is a polar plot illustrating the light distribution of the direct/indirect light fixture of FIG. 16.

FIG. 18 is a polar plot of the light distribution of the light fixture embodiment of FIG. 16 reconfigured with to remove the apertures in the reflector and create an indirect only embodiment.

FIG. 19 is a table of data comparing the performance of differing configurations of the light fixture embodiment of FIG. 16.

FIG. 20A is a cross-section view of a cove light fixture embodiment.

FIG. 20B is a sketch of a photometric plot representing the light distribution from the cove light fixture embodiment of FIG. 20A.

FIG. 21A is a cross-section view of a wall wash light fixture embodiment.

FIG. 21B is a sketch of a photometric plot representing the light distribution from the wall wash light fixture embodiment of FIG. 21A.

FIG. 22 is a cross-section view of a light fixture embodiment in which a gasket is fitted between the housing and optical element overhang to provide a seal with ingress protection.

DESCRIPTION

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing.

Embodiment configurations can be implemented in a wide range of light fixtures. One such fixture that benefits from advantages in aesthetic appearance, light distribution pattern, and luminous efficacy is shown in FIG. 1a The light fixture 100 a is mounted flush with ceiling tiles 200 a in a ceiling in a direct lit downlighting application. Alternatively, FIG. 1b shows an embodiment suspended direct/indirect light fixture 100 b which is mounted to hang below the ceiling 200 b and emit light out of both top and bottom output faces of the light fixture; in standard lighting industry terminology the downward light being considered “direct” and the upward light illuminating the ceiling considered “indirect”. Typical light fixture embodiments include LEDs as light sources and although the written descriptions may reference LED in the singular, typically an array of LEDS is used and should be implied if not explicitly stated or illustrated. Many types of reflectors may be used in various embodiments such as diffuse or specular reflectors or reflectors with surface features for redirection of incident light. Optical elements may contain surface features for purposes of light outcoupling, light redirection, or visual appearance. Arrays of features can be used such as a linear lenticular array which is often a suitable pattern.

For comparison with the embodiment A of FIG. 3, FIG. 2 shows a cross-section view of a lighting fixture having a conventional edge lit light guide. The housing 114 holds in place the LED board 102 with LED 101, light guide 103, reflector 108, and cover lens 111. The light guide 103 is a rectangular shaped sheet with an input face 104 and an output face 105 that are adjacent faces oriented at a 90 degree angle. Bezels 115A and 115B cover a significant portion of the ends of the light guide in order to hold the light guide and cover lens in place and also to mask hot spot non-uniformities near the input face of the light guide 103.

FIG. 3A and FIG. 3B show a cross-section view of embodiment A lighting assembly in which LED 1 light sources are mounted on an LED board 2 which providing a linear light source that inputs light into the optical element input face 4. Light propagates within the optical element 3 and is emitted from the output face 5. A portion of the light propagates directly through the optical element 3 on the direct transmission path 13 while concurrently a portion of the light propagates within the optical element on a TIR path 12 until it outcouples from the optical element 3. Means for outcoupling light are provided by lenticular surface 9 on the optical element opposing face 6 as well as by the light scattering composition of the bulk optical element 3. In embodiment A the light scattering composition is provided by polymer beads dispersed within an acrylic matrix material having a differing refractive index. Light outcoupling out the opposing face 6 is redirected toward the optical element output face 5 by the reflector 8.

The optical element 3 is comprised of a light transmissive material having a refractive index greater than the surrounding ambient environment; in the case of air >1. Optionally, regions of differing refractive index may be dispersed within the volume to scatter light and cause a portion of light to out couple from the optical element. Embodiment A is comprised of PMMA acrylic matrix with PMMA beads of differing refractive index dispersed throughout the volume. Other alternative materials for an optical element include but are not limited to clear or translucent grades of polycarbonate, cyclic olefin copolymers, silicone, and glass. PMMA acrylic has a refractive index of approximately 1.5 which in air produces a total internal reflection (TIR) critical angle of approximately 42 degrees. Dispersed light scattering regions within the optical element can be achieved by dispersing materials of differing refractive index throughout the material. Alternatively, 2^(nd) phase regions can be formed in-situ during processing of immiscible material blends.

The housing 14 encloses and holds in place optical components including the optical element 3, LED board 2, and if optionally present, the cover lens 11. The housing contains a bezel 15 feature which functions to cover the edge of the optical element including some or all of the optical element overhang 7.

The optical element input face 4 is inset from the outer perimeter of the optical element output face 5 and is angled so as to form an acute input/output face alignment angle 10, the angle being 70 degrees in the specific case of embodiment A. The acute input/output alignment angle functions to reduce “headlamp” type hot spots from the reflector 8 near the input face 4 and also increases the ratio of direct transmission to TIR light propagating within the optical element. The optical element overhang 7 provides a feature for mechanically securing the optical element in the housing 14 without excessively trapping light behind the bezel 15 as typically occurs in a conventional edge lit construction such as with the bezels 115A and 115B and input face 104 of FIG. 2. This functions to improve overall efficacy (lumens per watt) of the lighting system.

The cover lens 11 is an optional component which can be configured to enclose the output face of the light fixture and provide an appearance more uniform in brightness and color. Adjustments to the cover lens 11 surface geometry and bulk light scattering properties can be used to modify the output light distribution from that originating from the optical element output face 5. For example, adjustments to cover lens surface or volumetric light redirecting properties can be used to decrease the wide angle degree of lobes in the light distribution pattern or make brightness or color variations in the beam pattern emitting from the optical element output face more uniform. In the specific case of embodiment A, the surface is congruent with the shape of the cover lens and the bulk of the cover lens material has light scattering properties measured to have a symmetrical full width half maximum value of 68 when measured as a separate component on measurement equipment using as an input light source a narrow beam laser normal to the input surface.

FIG. 4 is a digital image of a Reference A light fixture representing a conventional edgelit light guide construction as shown in FIG. 2 but without a bezel or cover lens. FIG. 5 is a digital image of Embodiment A light fixture shown in FIG. 3A and FIG. 3B but without a bezel or cover lens. Both images were taken at a 45 degree viewing angle of the output face. Marked on the images are locations where line scans were analyzed to assess brightness levels corresponding to light directly transmitted through the light guide/optical element and light that does an initial reflection from the reflector near the input face. In the case Reference A, the initial reflection produces significant hot spot patterning commonly referred to as “headlamping” due to similarity in appearance of automotive headlamps projecting onto ground in front of a car. The headlamping effect is negligible in the FIG. 5 image of embodiment A.

FIG. 6 and FIG. 7 each show graphs and quantitative metrics characterizing brightness values along the line scan paths; FIG. 6 for direct transmission and FIG. 7 for initial reflection. For embodiment A, the direct transmission is significantly greater than reference A. In addition to the data of FIG. 6, this is evidenced by illumination measurements at 45 degrees comparing full optical light guide/optical element output vs. that with the output face masked except for the narrow band of direct transmission zone near the input edge. In this case, embodiment A direct transmission was 28% of full output at 45 degree angle while reference A direct transmission was 12% of total output at 45 degree angle.

FIG. 8 is a polar plot of embodiment A with one side only LED strip on and the light fixture oriented downward as a direct lit downlighting fixture. The cover lens is embodiment A is a diffusion lens characterized by a goniometric radiometer as having a symmetric FWHM of 68. This provides a large amount of light scattering that decreases the off axis orientation of light emitted from the optical element output face and produces a light distribution closer to lambertian. The amount of asymmetry in light distribution output can be controlled by selection of amount of light scattering in the cover lens to obtain a range of options between the “no cover lens” and “with cover lens” options illustrated in FIG. 9.

FIG. 9 is polar plot of embodiment A with LED strips on both sides of an optical element and the light fixture is oriented down as a direct lit downlighting fixture and shows a batwing type light distribution which can be adjusted to provide less asymmetry by increasing light scattering in the cover lens. The cover lens in embodiment A has a symmetric FHWM of 6868 which results in a very symmetric light distribution.

FIG. 10 is a cross section detail view of an embodiment with two optical elements configured to receive light from a central light source structure. Two LED boards 1002, are positioned upon a central light source mount 1016 to emit light from LEDs 1001 in opposing orientations into optical elements 1003, the result being a batwing type light output from the light fixture. The central light source mount also serves as a mounting ledge for the optical element overhang 1007 and also a bezel to mask from view the edge of the optical element, thereby appearing the uniformity appearance.

FIG. 11 is a cross section detail view of an embodiment with two optical element input faces 1104 positioned within a recessed cavity 1117. Two optical elements 1103 are configured to receive light from a central light source structure. Two LED boards 1102, are positioned upon a central light source mount 1116 to emit light from LEDs 1101 in opposing orientations, the result being a batwing type light output from the light fixture. The central light source mount also serves as a mounting ledge for the optical element overhang 1007 and also optionally a bezel 1115 to mask from view the edge of the optical element, thereby appearing the uniformity appearance. A cover lens 1111 may also be optionally positioned to further enclose the fixture and/or adjust light distribution or appearance.

FIG. 12 is a cross section view of a light fixture embodiment having an optical element input/output face alignment angle 1210 configured to direct a significant portion of direct transmission light 1213 out the optical element opposing face 1206 to be subsequently reflected off the reflector 1208 and back through the optical element 1203 and out the output face 1205. The light redirecting features 1209 on the output face 1205 function to redirect the optical path.

FIG. 13 is cross-section perspective view of a direct/indirect light fixture embodiment with an x-y profile geometry linearly extruded in the z-axis to create a generally rectangular fixture shape. Light from the LED 1301 on the LED board 1302 is received by the optical element input face 1304 of the optical element 1303 and propagates along a direct transmission path 1313, as illustrated by a single example light ray, and exits the optical element through optical element output face 1305 a then proceeds to transmit through the cover lens 1311 a resulting in upward light distribution which becomes part of the indirect light output of the fixture. The optical element 1303 contains light scattering regions which cause some portion of light to scatter enough to exceed the critical total internal reflection angle to outcouple out one of the two optical element output faces 1305 a and 1305 b and then subsequently through a cover lens 1311 a or 1311 b. In this embodiment light propagating out the bottom lens cover 1311 b is considered direct light fixture output while light propagating out the lens cover 1311 a is considered indirect light fixture output.

FIG. 14 is a cross-section perspective view of a direct/indirect light fixture embodiment with the x-y profile geometry is rotated to produce a generally circular shape fixture. Light from the LED 1401 on the LED board 1402 is received by the optical element input face 1404 of the optical element 1403 and propagates along a direct transmission path 1413, as illustrated by a single example light ray, and exits the optical element through optical element output face 1405 a then proceeds to transmit through the cover lens 1411 a resulting in upward light distribution which becomes part of the indirect light output of the fixture. The optical element 1403 contains light scattering regions which cause some portion of light to scatter enough to exceed the critical total internal reflection angle to outcouple out one of the two optical element output faces 1405 a and 1305 b and then subsequently through a cover lens 1411 a or 1411 b. In this embodiment light propagating out the bottom lens cover 1411 b is considered direct light fixture output while light propagating out the lens cover 1411 a is considered indirect light fixture output. The circular geometry enables some novel light distributions. In particular, elliptical (including circular) light distributions can be achieved. Typically the input face/output face alignment angle will be rotated 360 degrees which will be contribute to a circular light distribution. Variations in cover lens light redirecting features can contribute to more elliptical light distributions; for example, if there are an array of linear lenticular features the features will direct light differently at differing input angles.

FIG. 15 is a cross-section perspective view of a direct/indirect light fixture embodiment having 2 input faces with differing optical element input face/output face alignment angles. Optical element input face 1504 a and optical element output face 1505 b create a 90 degree optical element input face/output face alignment angle 1510 a. In contrast, optical element input face 1504 b and optical element output face 1505 b create an optical element input face/output face alignment angle 1510 b of 110 degree which produces an optical element that projects more light out optical element output face 1505 a and cover lens 15111 a in an upward indirect direction of the light fixture than through the downward direct light fixture direction wherein light escapes the optical element 1503 through the optical element output face 1505 b and subsequently through the cover lens 1511 b. Each input face of the optical element is aligned with an LED board 1501 with LED 1502 and with each LED board mounted onto a housing 1514.

FIG. 16 is a cross-section perspective view of a direct/indirect light fixture embodiment with light input into two sides of the light fixture. The two sides are mirror images of each other so the following description applies to light input into the optical embodiment from both sides. Light from the LED 1601 on the LED board 1602 is received by the optical element input face 1604 of the optical element 1303 and propagates along a direct transmission path 1613, as illustrated by a single example light ray, and exits the optical element through optical element output face 1605 a resulting in upward light distribution which becomes part of the indirect light output 1619 of the fixture. The optical element 1603 contains light scattering regions which cause some portion of light to scatter enough to exceed the critical total internal reflection angle to outcouple out one of the two optical element output faces 1605 a and 1605 b. The housing 1614 contains apertures 1620 on the bottom of the fixture which are openings in both the housing 1614 and reflector 1608 through which a portion of the total light output is transmitted. In this embodiment light propagating out the bottom of the fixture is considered direct light fixture output 1618 while light propagating upward is considered indirect light fixture output 1619. Alternative embodiments may contain a cover lens over the top or bottom of the fixture to enclose and/or further direct light to further adjust light distribution or visual appearance.

FIG. 17 is a polar plot illustrating the measured light distribution of the direct/indirect light fixture embodiment of FIG. 16. Both indirect (upwards) and direct (downwards) light distributions are of a symmetrical batwing type useful for even illumination when projected onto flat target illumination surfaces such as ceiling, floors, and table tops. 14% of light is downward direct light fixture output and 86% is upward indirect light fixture output. Asymmetric embodiments are easily configured by adjusting to differ the amount of electrical power the power applied to the two using only a LED board on a single side of the optical element.

FIG. 18 is a polar plot of the measured light distribution of a light fixture embodiment of FIG. 16 reconfigured to remove the apertures in the reflector and create an indirect only embodiment. In this embodiment, the reflector 1608 does not have apertures but rather extends to cover the entire bottom side of the optical element.

FIG. 19 is a table of data comparing the performance of differing configurations of the light fixture embodiment of FIG. 16 and summarizes optical performance of high efficacy, light distribution, and a high ratio of indirect to direct light fixture output.

FIG. 20A is a cross-section view of a wall cove_fixture embodiment. An optical element 2003 receives light from an LED 2001 mounted on an LED board 2002 at an optical element input face 2004. The LED board 2002 is mounted within the housing 2014 and has on the opposite side from the LED an electrical connector 2021. The backside placement of the electrical connector allows the frontside with LED to maintain a flat plane for mounting flush to the housing. Light entering the optical element 2003 at the input face 2004 propagates through the optical element by a combination of direct transmission and TIR paths before outcoupling out the optical element output face 2005. Light that exits the light guide from the optical element opposing face 2006 reflects off the reflector 2008 and propagates back through optical element to exit out the output face 2005. The wedge shape of the optical element 2003 improves efficacy and uniformity by gradually decreasing the cross-sectional area available for TIR.

FIG. 20B is a sketch of a photometric plot representing the light distribution from the cove light fixture embodiment of FIG. 20A. The asymmetric light distribution is well suited for a cove lighting application wherein the light fixture is typically mounted horizontally near a wall/ceiling interface.

FIG. 21A is a cross-section view of a wall wash fixture embodiment. An optical element 2013 receives light from an LED 2101 mounted on an LED board 2102 at an optical element input face 2104. The LED board 2102 is mounted within the housing 2114 and has on the opposite side from the LED an electrical connector 2021. The backside placement of the electrical connector allows the frontside with LED to maintain a flat plane for mounting flush to the housing. Light entering the optical element 2103 at the input face 2104 propagates through the optical element by a combination of direct transmission and TIR paths before outcoupling out the optical element output face 2105. Light that exits the light guide from the optical element opposing face 2106 reflects off the reflector 2108 and propagates back through optical element to exit out the output face 2105. The wedge shape of the optical element 2103 improves efficacy and uniformity by gradually decreasing the cross-sectional area available for TIR.

FIG. 21B is a sketch of a photometric plot representing the light distribution from the wall wash light fixture embodiment of FIG. 21A. The asymmetric light distribution is well suited for a wall wash application wherein the light fixture is typically mounted vertically with the optical element output face substantially parallel to a wall surface.

FIG. 22 is a cross-section view of a light fixture embodiment with reflector 2208 in which a gasket 2205 is fitted between the housing 2214 and optical element 2203 overhang to provide a seal with ingress protection. The location of the gasket 2205 set back from the LED board 2202 with LED 2001 minimizes blockage of light output from the output face 2204 and can be an advantage in both efficacy and visual appearance. 

What is claimed is:
 1. A light fixture comprising; a) a first optical element having an input face perpendicular to a x-y profile cross-section, an output face perpendicular to a x-y profile cross-section, and an optical element overhang which extends beyond the input face; b) a first light source aligned perpendicular to the z axis of the optical element which emits light into the input face of the optical element; wherein a portion of light is directly transmitted from the input face through the output face and a portion of light is propagated within the optical element by total internal reflection at the output face.
 2. The light fixture of claim 1 having the input face and the output face arranged with the input face/output face alignment angle substantially less than 90 degrees within a x-y cross-sectional plane aligned with the optical output axis of the light source aligned perpendicular to the z axis of the optical element which emits light into the input face of the optical element.
 3. The light fixture of claim 2 wherein the input/output face alignment angle preferentially directs more light to the output surface and less light to a second output surface.
 4. The light fixture of claim 1 further comprising a second optical element joined to the first optical element by means of the optical overhang.
 5. The light fixture of claim 1 further comprising a second optical element and second light source positioned as a mirror image of the first optical element and first light source.
 6. The light fixture of claim 5 further comprising a cover panel positioned adjacent to the junction between the first and second optical elements.
 7. The light fixture of claim 1 wherein the 3 dimensional shape of the optical element is a x-y cross-sectional profile extended linearly into a z axis.
 8. The light fixture of claim 1 wherein the 3 dimensional shape of the optical element is a x-y cross-sectional profile extended rotationally into a z axis to produce circular geometry.
 9. The light fixture of claim 8 further comprising a cover lens with linear lenticular features wherein the light fixture output is an elliptical light distribution.
 10. The light fixture of claim 1 further comprising a second light source aligned perpendicular to the z axis of the optical element which emits light into a second input face of the light guide.
 11. The light fixture of claim 1 further comprising a reflector mounted adjacent to an optical element face opposing the output face.
 12. The light fixture of claim 11 further comprising one or more apertures in the reflector to enable a direct/indirect light distribution.
 13. The light fixture of claim 1 further having direct/indirect light fixture output.
 14. The light fixture of claim 1 wherein the optical element is a wedge shape.
 15. The light fixture of claim 1 configured for a cove lighting application.
 16. The light fixture of claim 1 configured for a wall washing application.
 17. The light fixture of claim 1 further comprising a cover lens mounted proximate to the optical element output face.
 18. The light fixture of claim 17 wherein the cover lens further comprises light redirecting features.
 19. The light fixture of claim 1 installed in a ceiling.
 20. The light fixture of claim 1 mounted flush with ceiling tiles in a suspended ceiling grid system.
 21. The light fixture of claim 1 wherein the optical element is rectangular shaped in the x-z plane.
 22. The light fixture of claim 1 that is rectangular shaped.
 23. The light fixture of claim 1 having a circular geometry.
 24. The light fixture of claim 1 wherein a portion of light that is propagated within the optical element by total internal reflection subsequently exits at the output face.
 25. The light fixture of claim 1 wherein the optical element further comprises light scattering particles.
 26. The light fixture of claim 1 further comprising a gasket between optical element and housing to provide ingress protection. 